: >...just in case you're not sure how to connect it, I tie one end of the : >modulation transformer (that WAS going to the B+ supply) to ground. : >The other side is connected to a large capacitor (5uf @ 5kV) on the Final : >side of the B+ line to the final. : > : >So, from the B+ supply, attach to one side of the choke, the capacitor to : >the other side, that's connects to the mod xfmr and then B+ from the choke : >to the final. This shunts the DC off of the secondary of the modulation : >transformer, allows the transformer to react more linearly, and prevents : >core saturation on the secondary of the modulation transformer. : >More Core in the transformer = broader range of frequencies, generally : >speaking. : : Actually there are 3 ways to connect it. The above corfiguration has the : disadvantage that one winding of the modulation transformer is always : grounded, putting high voltage stress on the insulation between windings.
the alternative to that, is to put another capacitor from the low-end of the modulation transformer, to ground. Just to be clear, Don - I'm shunting, entirely, the DC off of the secondary of the modulation transformer. Capacitivly coupling the transformer coupled audio to the B+ line, on the 'high' end (or the tank circuit end) of the reactor choke. : You can use a string of filter chokes in series, but that is bulky, and : sometimes power supply chokes have so much stray capacitance that you lose : high frequency response. Ask me or John, WA5BXO sometime to explain how we : made a nice compact mod reactor @ 30 Henries using two identical 12-Henry : filter chokes. I've been there, seen it, held it in my hands, when I went there and helped John put the rig together, when he bought the trailer and put it on the property there at Delta Plaza. Then the floods came in, and floated the trailer, and bounced it around the pylons under I-45 where it crosses Spring Creek, finally cracking the trailer open like an egg, with the force of the water. : With so many old tube type BC transmitters being junked as they are replaced : by solid state units, modulation ractors and transformers should not be that : hard to find. I need to keep looking, then. I'm just trying to get something going, with what I've got. I -have- been working on a modulator deck. Building it up, using the configuration as a combination deck, that'll handle either 250TH's or 450TL's. some pictures (so far) of the rebuild are at http://w5omr.shacknet.nu:81/~w5omr/250-rebuild/ 73 = Best Regards, -=Jeff/W5OMR=-
